PHOENIX (AP) – For more than a year, Phoenix police were stumped by a string of killings in which a shooter stalked victims after dark and gunned them down as they stood outside their homes or sat in their cars.

Nine people were killed in all in a case dubbed the Serial Street Shooter.

Police fielded thousands of tips, went door-to-door in a largely Hispanic neighborhood of Phoenix where the shootings happened and analyzed ballistics from a different, unrelated serial shooting case.

On Monday, they announced they had arrested Aaron Juan Saucedo, 23, a former city bus driver, in the killings while providing scant detail about what motivated him or details about how they made a break in the case, other than to credit tips.